Adverse effects of prenatal mercury exposure on neurodevelopment during the first 3 years of life modified by early growth velocity and prenatal maternal folate level.

BACKGROUND AND AIMS: Previous studies have suggested that mercury exposure and folate levels during pregnancy may influence early childhood neurodevelopment. Rapid catch-up growth in children is associated with an increased risk of pathological nervous system development. We evaluated whether the association between prenatal folate and mercury-related neuropsychological dysfunction was modified by growth velocity during childhood. METHODS: The Mothers and Children's Environmental Health (MOCEH) birth cohort study began in 2006 and by 2010, 1751 women had been enrolled before the second trimester of their pregnancy along with their partners. Participants visited the research center at birth and 6, 12, 24, and 36 months. We measured mercury levels in maternal and cord blood and folate in maternal serum. Questionnaires to evaluate the environment and health of their child were administered and anthropometric factors including body weight and height were measured. Certified investigators used the Bayley test to measure neurobehavioral outcomes. We calculated postnatal growth change as the change in infant weight for-age z-score between birth and 3 years. Multiple linear regression and mixed models were used to examine the association between mercury exposure and children's neurodevelopment as well as the modifying effects of folate and growth velocity. RESULTS: A total of 30.6% of children experienced rapid growth during the first 3 years of life. Median values of mercury in the low folate group were significantly higher in rapid growers (3.41 µg/L in maternal blood and 5.63 µg/L in cord blood) than in average/slow growers (3.05 µg/L in maternal blood and 5.19 µg/L in cord blood). Rapid growers were also significantly associated with decreased psychomotor development scores during the first 3 years of life and with having mothers who had low prenatal folate levels, even after adjusting for potential confounders. CONCLUSION: Prenatal mercury exposure adversely affects infant neurodevelopment and is associated with rapid growth during the first 3 years of life. This effect was limited to children whose mothers had low prenatal folate levels, suggesting a protective effect of folate against developmental neurotoxicity due to mercury exposure and rapid catch-up growth.

The Mothers and Children's Environmental Health (MOCEH) study.

The MOCEH study is a prospective hospital- and community-based cohort study designed to collect information related to environmental exposures (chemical, biological, nutritional, physical, and psychosocial) during pregnancy and childhood and to examine how exposure to environmental pollutants affects growth, development, and disease. The MOCEH network includes one coordinating center, four local centers responsible for recruiting pregnant women, and four evaluation centers (a nutrition center, bio-repository center, neurocognitive development center, and environment assessment center). At the local centers, trained nurses interview the participants to gather information regarding their demographic and socioeconomic characteristics, complications related to the current gestation period, health behaviors and environmental factors. These centers also collect samples of blood, placenta, urine, and breast milk. Environmental hygienists measure each participant's level of exposure to indoor and outdoor pollutants during the pre- and postnatal periods. The participants are followed up through delivery and until the child is 5 years of age. The MOCEH study plans to recruit 1,500 pregnant women between 2006 and 2010 and to perform follow-up studies on their children. We expect this study to provide evidence to support the hypothesis that the gestational environment has an effect on the development of diseases during adulthood. We also expect the study results to enable evaluation of latency and age-specific susceptibility to exposure to hazardous environmental pollutants, evaluation of growth retardation focused on environmental and genetic risk factors, selection of target environmental diseases in children, development of an environmental health index, and establishment of a national policy for improving the health of pregnant women and their children.